Riot Games API proxy on Cloudflare Workers

RiotGamesApiProxyWorker.js

addEventListener("fetch", (event) => {
  event.respondWith(
    handleRequest(event).catch(
      (err) => new Response(err.stack, { status: 500 })
    )
  );
});

/**
 * Many more examples available at:
 *   https://developers.cloudflare.com/workers/examples
 * @param {Request} request
 * @returns {Promise<Response>}
 */
async function handleRequest(event) {
    const request = event.request
    const cacheUrl = new URL(request.url)
    const cacheKey = new Request(cacheUrl.toString(), request)
    let cache = caches.default
    let response = await cache.match(cacheKey)

    if (response) {
        console.log(`Cache hit for: ${request.url}.`)
        return response
    } else {    
        console.log(`Response for request url: ${request.url} not present in cache. Fetching and caching request.`)

        try {
            response = await sendToRiot(request)            
            // Clone the response so that it's no longer immutable
            response = new Response(response.body, response)

            if (response.status == 200 && // Only cache 200 responses (not rate limits etc)
                !request.url.endsWith('lol/spectator/v4/featured-games')) { // Don't cache featured games
                response.headers.set("Cache-Control", "max-age=600, stale-while-revalidate=60, stale-if-error=86400, must-revalidate")
                // NOTE: waitUntil does NOT block / wait
                event.waitUntil(cache.put(cacheKey, response.clone()))
            }
        } catch (e) {
            return new Response(JSON.stringify({ error: e.message }), { status: 500 })
        }
    }

    if (request.headers.get('CF-Connecting-IP') == DEVELOPER_IP) {
        // Allow localhost etc.
        response.headers.set("Access-Control-Allow-Origin", "*")  
        // Allow whatever headers are set (CORS).
        response.headers.set("Access-Control-Allow-Headers", request.headers.get("Access-Control-Request-Headers"))
    } else {
        response.headers.delete("Access-Control-Allow-Origin")
        response.headers.delete("Access-Control-Allow-Methods")
        response.headers.delete("Access-Control-Allow-Headers")
        response.headers.delete("Access-Control-Expose-Headers")
    }
    
    // Create an identity TransformStream (a.k.a. a pipe).
    // The readable side will become our new response body.
    let { readable, writable } = new TransformStream()

    // Start pumping the body. NOTE: No await!
    response.body.pipeTo(writable)
    
    return new Response(readable, response)
}

async function sendToRiot(request) {
    const { pathname } = new URL(request.url)
    // Assumes the path is in the format /euw1/lol/spectator/v4/featured-games. If /api/euw1/... change both 1's to 2's below.
    const url = new URL("https://" + pathname.split("/")[1] + ".api.riotgames.com" + pathname.substring(pathname.indexOf('/', 1)))
    console.log("Riot API URL: " + url.toString())
    const newRequest = new Request(url.toString(), request)
    newRequest.headers.set("X-Riot-Token", RIOT_TOKEN)
    return await fetch(newRequest)
}

Set RIOT_TOKEN to your token and DEVELOPER_IP to your IP address, as environment variables in the worker settings.
Featured Games will bypass the CF cache.